1. Field of the Invention
The present invention relates to digital data storage systems. More particularly, the invention concerns a data storage system with an outboard data manager that performs data management operations without requiring substantial host involvement. Some exemplary data management operations include copy, migrate, move, recall, restore, defragment, reorganize, and the like.
2. Description of the Related Art
The manipulation, exchange, and storage of data are central functions in this information age. In a data storage system, there are many reasons to transfer data from one storage device to another. For example, many prudent computer users make duplicate or "backup" copies of their data to protect against data loss. Some other examples of data transfer operations are data reclamation, de-fragmentation, migration, etc. These generally involve some variation of copying data or moving data, where a data "move" entails a copy operation followed by the deletion of the source data from its original location.
To illustrate a common technique for data transfer, FIG. 1 shows a typical data storage system 100. The system 100 includes a host 102 coupled to a controller 104 and a controller 108. The host 102 includes one or more processors that manage the controllers 104, 108.
The controllers 104, 108 also include processing features, and serve to more specifically manage the operation of respective storage devices 106, 110. Namely, the controller 104 is coupled to the data storage unit 106, which contains source data to be moved or copied. The controller 108 is coupled to a second data storage unit 110, which is the destination for the data transfer operation. The storage devices 106, 110 may comprise one or more magnetic hard drives, tape drives, libraries, or other digital data storage devices.
To copy data from the source 106, the host 102 directs the controller 104 to copy source data from the device 106 and pass this data back to the host 102. The host 102 forwards the data to the controller 108, and directs the controller 108 to coordinate storage of the copied data at the target 110. In the case of a data move, the source data is deleted after verifying that the copy operation has succeeded.
Although the foregoing backup technique is used widely, and some users may find this approach to be completely satisfactory, engineers at International Business Machines are continually seeking ways to improve data storage systems. One area of possible improvement concerns the processing burden experienced by the host 102 during data transfer operations. Particularly, the host 102 must serve as a conduit between the controllers 104, 108, which actually oversee the storage and retrieval of data from the devices 106, 110. This can involve a significant burden on the input/output ("I/O") and processing capabilities of the host 102, at the expense of application programs running on the host. In most cases, these application programs are the central functions of the system 100, such as database management, mathematical modeling, financial analysis, network support, and other applications. Therefore, interruption of important processing tasks of the host 102 may be undesirable in many cases. Consequently, in some applications, known data copy and transfer systems are not completely adequate.